MUNICH - German prosecutors said on Wednesday they had filed charges against former Audi Chief Executive Rupert Stadler, who is being investigated over his role in Volkswagen's emissions test cheating scandal.

Volkswagen admitted in September 2015 to having used illegal engine control software to cheat pollution tests, triggering a global backlash against diesel. The affair has so far cost the German carmaker 30 billion euros ($33.5 billion).

The public prosecutor's office in Munich said Stadler and three other defendants are being charged with fraud, false certification and criminal advertising practices. Stadler has denied any wrongdoing, his lawyer said.

Premium brand Audi only admitted in November 2015 that its 3.0 litre V6 diesel engines were fitted with an auxiliary control device which was deemed illegal in the United States.

Volkswagen and its former managers have faced numerous law suits, and in April prosecutors in the German city of Braunschweig charged former Volkswagen boss Martin Winterkorn with fraud over his role.

The Munich prosecutor said that three of the defendants are accused of having developed engines for Audi, Volkswagen and Porsche cars that used emissions cheat devices.

"Defendant Stadler is accused of having been aware of the manipulations since the end of September 2015 at the latest, but he did not prevent the sale of affected Audi and VW vehicles thereafter," the prosecutor said in a statement.

Stadler was arrested in June 2018 as part of a broader probe into emissions cheating at Audi, which is part of Volkswagen Group, and spent several months in prison.

Volkswagen later terminated Stadler's contract against the backdrop of a criminal investigation into whether he was involved in emissions tests cheating.

The prosecutors said that his indictment relates to roughly 250,000 Audi branded cars, 112,000 Porsches and 72,000 Volkswagen cars that were sold in the U.S. and Europe.

'PRESUMPTION OF INNOCENCE'

The defendants charged by the Munich prosecutor include former Audi and Porsche manager Wolfgang Hatz as well as two engineers, several people familiar with the proceedings said.

Hatz, former research and development chief at Porsche and former head of powertrain development at Audi and parent Volkswagen, spent several months in custody in 2017 and 2018 over his alleged role in the emissions cheating scandal.

A lawyer for Hatz separately said his client denied any wrongdoing.

The Munich prosecutors on Wednesday declined to identify the defendants, except for Stadler.

Investigations against 23 further suspects continue, the prosecutor's office said.

The Braunschweig prosecutors had said that Volkswagen's emissions cheating took place between November 2006 and September 2015, and that Winterkorn failed in his duty to inform European and U.S. authorities after it became clear in May 2014 that diesel engines had been manipulated.

Winterkorn had also neglected to inform customers of, and did not prevent, the continued installation of fraudulent software, the prosecutors have said.

Winterkorn's lawyer has said he cannot comment on the charges because he had been denied access to important case files.

Audi said in a statement on Wednesday that it was in the interest of the company, its shareholders and employees to clarify the issues that led to the diesel crisis.

"Until this has happened, the presumption of innocence must prevail," the spokesman said.

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